Tried that. Tried calling a shell script instead that contained the rsync. Tried changing the script to simply redirect ls of my home directory into a file there. In every case, what I see in the system log is the same:

Another frustrating evening with launchd. Adapted your version of the plist to my environment. Learned about extended file attributes and how to remove them. Now my job just returns 255. Can't tell why of course.

After a little digging I think the 255 error code is coming from rsync (unexplained error from googling) and I ran across this page which details logging stdout and stderr from launchd which might give you a clue as to what's going wrong.